We present the discovery and phase-coherent timing of four highly dispersed millisecond pulsars (MSPs) from the Arecibo PALFA Galactic plane survey: PSRs J1844+0115, J1850+0124, J1900+0308, and J1944+2236. Three of the four pulsars are in binary systems with low-mass companions, which are most likely white dwarfs, and which have orbital periods on the order of days. The fourth pulsar is isolated. All four pulsars have large dispersion measures (DM >100 pc cm–3), are distant (3.4 kpc), faint at 1.4 GHz ( 0.2 mJy), and are fully recycled (with spin periods P between 3.5 and 4.9 ms). The three binaries also have very small orbital eccentricities, as expected for tidally circularized, fully recycled systems with low-mass companions. These four pulsars have DM/P ratios that are among the highest values for field MSPs in the Galaxy. These discoveries bring the total number of confirmed MSPs from the PALFA survey to 15. The discovery of these MSPs illustrates the power of PALFA for finding weak, distant MSPs at low-Galactic latitudes. This is important for accurate estimates of the Galactic MSP population and for the number of MSPs that the Square Kilometer Array can be expected to detect.

The authors acknowledge support from the NSF grant AST-0807151, NSERC Discovery Grants, FQRNT via the Centre de Recherche Astrophysique du Quebec, CIFAR, CANARIE, Compute Canada, the Canada Foundation for Innovation, a Killam Research Fellowship, an NWO Veni Fellowship, the Max Planck Society, an NSERC PGS scholarship, an IMPRS fellowship, and the European Research Council for the ERC Starting Grant BEACON under contract No. 279702.